Device for positioning and guiding a surgical instrument during orthopaedic interventions

ABSTRACT

The invention relates to a device for positioning and guiding a surgical instrument during orthopaedic interventions, comprising an industrial robot which has a program-controlled robot arm ( 1 ) with several articulated joints and a mounting plate ( 2 ) at the end of said arm, an instrument ( 3 ) for the orthopaedic intervention attached to the mounting plate ( 2 ) and a program control with computer. Sensors for detecting the position of the joints in an instrument-coordinating system defined in the program control are situated in the joints of the robot arm ( 1 ). According to the invention, a manually guided sensor device, for example in the form of a sensor arm ( 4 ) with multiple joints, is used for the three-dimensional measurement of an object by the instrument-coordinating system of the industrial robot. Using the sensor device ( 4 ), and with a previously adopted basic position of the robot arm ( 1 ) specified by the program control, reference points can be detected on the bone of the patient. From the coordinates of the reference points related to the instrument-coordinating system the computer calculates a working position, which the robot arm ( 1 ) subsequently assumes during the surgical intervention.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage of PCT/EP97/07186 filed Dec. 19,1997 and based upon German national application 19653966.8 of Dec. 21,1996 under the International Convention.

FIELD OF THE INVENTION

The present invention relates to a device for positioning and guidanceof a surgical instrument during orthopaedic operations, with

an industrial robot having a program-controlled multi-jointed robot armwith a mounting plate on its end,

an instrument for the surgical procedure held on the mounting plate, and

a program control system with computer, whereby sensors are arranged inthe joints of the robot arm to determine the joint positions in aninstrument coordinate system in the program control system and wherebythe robot arm can be moved by means of the program control system to aworking position for the surgical procedure.

BACKGROUND OF THE INVENTION

A device with the features described above is known from the Jul. 29,1994 issue of VDI Nachrichten and is used in hip operations. Before theoperation, three screws are initially implanted into the patient's kneeand the thigh bone. The screws have a slight indentation into which fitsthe head of a feeler arranged at the end of a robot arm. A computertomograph also carried out before the operation provides necessarypatient data for the program control system. During the surgicalprocedure, the patient's thigh is clamped in a sterile holder arm thatis rigidly attached to the foot of the industrial robot. A measuring armplaced on the bone records any positional changes. Firstly, the surgeonleads the robot arm with the feeler at its end to the reference pointsgiven by the indentations in the screws, the coordinates of which arecompared with the data from the tomograph. From the data, the computerthen determines the working position of the robot arm for the surgicalprocedure. Once the working position has been determined, the feeler isreplaced by an instrument and the femur shaft is milled usingappropriate feed movements of the robot arm under program control. Next,the surgeon can insert a previously selected prosthesis.

The application of the known device requires extensive preoperativeplanning and use of computer tomography, which are not only expensive,but also prolong the operation time to an overall extent that isproblematic. Also unfavorable is the fact that the surgeon has nopossibility of exerting an influence on the program-controlled course ofthe operation. In the event of positional changes of the bone and/ornon-compliance with predetermined tolerances, the device immediatelyinterrupts its work for safety reasons.

OBJECT OF THE INVENTION

The object of the invention is to provide a device of the type describedat the outset, which is deployable intraoperatively and so designed thatthe surgeon can exercise an influence on the operation.

SUMMARY OF THE INVENTION

According to the invention the object is achieved in that a sensorarrangement manually controllable independently of the position of therobot arm is provided for three-dimensional object measurement in theinstrument coordinate system of the industrial robot, such that, bymeans of the sensor arrangement, using a previously-assumed homeposition of the robot arm prescribed by the program control system,reference points on the patient's bone can be sensed and the computerdetermines the working position of the robot arm from the coordinates ofthe reference points related to the instrument coordinate system. It istaken that the working position of the robot arm can also include asequence of robot arm positions, which must be visited in order to guideand position optimally the instrument arranged on the mounting plate forthe execution of the surgical procedure. Independently of the technicalimplementation of the sensor arrangement, it is of fundamentalsignificance to the invention that through a coupling of the sensorarrangement and the robot arm, which can be realized in differing waysexplained in greater detail below, the coordinates of the referencepoints in the instrument coordinate system of the industrial robot aredetermined, this being defined in the program control system.

The sensor arrangement allows a sufficient number of clearlyidentifiable reference points on the patient to be determined for thecalculation of the working position of the robot arm. During recordingof these reference points, the robot arm remains stationary in thepreviously assumed known home position. Using the coordinates of thehome position and the coordinates of the reference points, the workingposition that the robot arm subsequently assumes during the surgicalprocedure can be calculated exactly. Depending on the type of surgicalprocedure, a single working position or a sequence of working positionsis determined. The device according to the invention permitsintraoperative application. Preoperative planning on the basis, forexample, of X-ray photographs or computer tomographs is not required inprinciple. Furthermore, the program control system can be set up sothat, during the operation on bones that are exposed during theprocedure, the surgeon records further characteristic points with theaid of the sensor arrangement, which are then processed for correctionof the working position of the robot arm and/or to determine a sequenceof working positions which the robot arm assumes one after the other asthe operation proceeds.

According to the invention, it is possible to employ sensor arrangementsbased on various measuring principles. One embodiment consists of amulti-jointed manually moveable sensor arm connected to the mountingplate of the robot arm. The coupling to the instrument coordinate systemof the robot is achieved in this case through a rigid mechanicalconnection, so that the fixing of the sensor arm on the mounting platemust take place precisely at an exactly defined position. The sensor armhas joints with sensors to detect the joint positions. By manualguidance of the sensor arm at a predetermined and previously assumedhome position of the robot arm, reference points on the patient's bonecan be sensed, the coordinates of which are passed to the computer. Fromthese coordinates, the computer determines the working position of therobot arm. A sensor arm with six joints is preferable.

Multi-jointed sensor arms having sensors to determine the jointpositions are already known. These are passive, exclusively manuallysteerable measuring instruments, which are used, within the scope ofknown techniques, as transportable devices for measuring workpieces. Theinvention starts with the recognition that the attachment of amulti-jointed sensor arm to the end of a program-controlled active robotarm brings significant advantages that can be utilized in surgicalprocedures. Of fundamental significance to the invention is the factthat the sensor arm arranged on the mounting plate is not replaced byinstruments, but is available to the surgeon throughout the entiresurgical procedure.

A further embodiment of the invention provides for the sensorarrangement consisting of a multi-jointed sensor arm connected to thecomputer, the arm being spatially so arranged that both the patient'sbone to be sensed and the mounting plate of the robot arm placed in ahome position are within the working space measurable with the sensorarm, such that with the aid of the sensor arm, at least one referencepoint on the mounting plate can be sensed so that, by means of thesensor arm, both the position and orientation of the mounting plate andthe reference points sensed on the patient's bone are determined in afixed three-dimensional coordinate system and such that the computertransforms the spatial coordinates found into the coordinates of theinstrument coordinate system. Multiple points may be provided on themounting plate, the positions of which are exactly defined and have beendetermined in relation to the instrument coordinate system. Anotherpossibility consists in moving the robot arm not only to one, butsequentially to several, and at least three, home positions. At each ofthese home positions, in each case only one point defined on themounting plate is sensed with the sensor arm. In the spatial coordinatesystem of the sensor arrangement, this point then has differentcoordinates for each home position of the robot arm. Given thesecoordinates, the subsequently sensed spatial coordinates of thereference points on the bone can be transformed into the instrumentcoordinate system.

A further possibility for implementation of the sensor arrangementprovides for use of a three-dimensional locating system which locatesobjects through the interaction of transmitter/receiver elements.Systems of this type are known in principle and can be based on optical,inductive or ultrasonic processes. According to the invention, thesensor arrangement in this case consists of a measuring arrangement withremote data transmission having a stationary receiver, a sensing probewith a first transmitter, and a second transmitter arranged on themounting plate, such that the transmitters have multiple signalgenerators in a rigidly defined spatial arrangement which emitpositioning signals that are received by the receiver, such that theposition and orientation of the sensing probe and of the mounting platein a spatially fixed three-dimensional coordinate system are determinedfrom the positioning signals and such that the spatial coordinates foundfor the sensing probe and mounting plate can be passed to the computer,which transforms the spatial coordinates of the sensing probe into thecoordinates of the instrument coordinate system.

Finally, within the scope of the invention, it is possible to employ ameasuring arrangement with remote data transmission as a sensorarrangement having a stationary receiver and a sensing probe with atransmitter, such that the transmitter has several signal generators ina rigidly defined spatial arrangement which emit positioning signalsthat are received by the receiver, such that, with the aid of thesensing probe, at least one reference point on the mounting plate of therobot arm moved into a home position can be sensed, such that both theposition and orientation of the mounting plate and of the referencepoints sensed on the patient's bone are determined in a spatially fixedthree-dimensional coordinate system by means of the sensing probe, andsuch that the computer transforms the spatial coordinates determinedinto the coordinates of the instrument coordinate system.

According to the invention the computer develops an executable robotprogram from the coordinates of the reference points input with thesensor arm or the locating system, which is transferred to the programcontrol system, such that the bone processing is undertaken underprogram control through a movement of the robot arm. According to apreferred embodiment of the invention, however, the instrument for thesurgical procedure is guided on a carriage also affixed to the mountingplate, and is movable axially. With this embodiment of the invention,the feed movement of the surgical instrument can be carried out by thesurgeon manually or with a motorized feed drive independently of themovement of the robot arm, once the surgical instrument has been placedby the device according to the invention in an optimum position andoptimum orientation for the operation. This embodiment of the inventionpermits short operation times, such that the cuts to be performed cannevertheless be carried out very precisely, because the instrument isoptimally held and guided by the device according to the invention.

The device can have an additional monitoring arrangement to determinethe spatial position of the patient during the operation. The technicalconfiguration of this monitoring arrangement is dependent on thelocating system used. In the embodiment with a sensor arm, a camera isemployed which detects the position of marking pegs that have beeninserted into the relevant bone before the surgical procedure and thecoordinates of which are sensed with the aid of the sensor arm whensetting up the working position of the robot arm, such that positionalchanges of the marking pegs detected by the camera are processed in thecomputer and a correction of the working position of the robot arm isundertaken by the program control system. With utilization of a sensorarrangement with transmitter and receiver elements, the monitoringarrangement preferably has at least one reference peg, which can beaffixed to the relevant bone of the patient before the surgicalprocedure and is equipped with a transmitter, such that the referencepeg transmitter has several signal generators in a suitable manner,similarly to the sensing probe, which emit positioning signals that arereceived by the receiver. The bone can be located exactly and itsposition calculated precisely. In the event of the bone's positionchanging, an automatic positional adjustment of the robot arm and of thesurgical instrument attached to the robot arm is made, this possiblyrequiring authorization by the surgeon.

BRIEF DESCRIPTION OF THE DRAWING

The invention is now described with reference to the accompanyingdrawing, in which

FIG. 1 shows sections of a plan view of a device for the positioning andguidance of a surgical instrument during orthopaedic operations,

FIG. 2 shows the side elevation A in FIG. 1,

FIG. 3 shows the side elevation B in FIG. 1, and

FIGS. 4 and 5 show further embodiments of the device according to thepresent invention schematically.

SPECIFIC DESCRIPTION

The fundamental structure of the device includes an industrial robothaving a multi-jointed, program-controlled robot arm with a mountingplate at its end, as well as a program control system with a computer.In the joints of the robot arm, there are sensors to detect the jointpositions. The robot arm can be moved by means of the program controlsystem to a working position for the surgical procedure.

In FIGS. 1 to 3, only the free end of the robot arm 1 is shown. It has amounting plate 2 at its end, to which are attached an instrument 3 forthe orthopaedic procedure, as well as a multi-jointed, manually movablesensor arm 4. A comparison of FIGS. 1 and 2 reveals that the sensor arm4 has at least three joints 5. Preferably there are six joints. Thejoints 5 have sensors, e.g. in the form of potentiometers, incrementalposition transducers, resolvers or the like, for determining the jointpositions. With manual guidance of the sensor arm 4 at a home positionof the robot arm 1 given by the program control system, reference pointson the patient's bone can be sensed and their coordinates passed to thecomputer (not shown). From the coordinates, the computer calculates theworking position that the robot arm 1 then assumes during the surgicalprocedure.

A comparison of FIGS. 1 and 3 reveals that the instrument 3 is movablyguided axially on a carriage 6 also attached to the mounting plate 2.The carriage 6 is arranged to move orthogonally to the mounting plate 2.The feed movement of the instrument 3 can be carried out manually orwith a motorized feed drive independently of the movement of the robotarm 1.

With the embodiment shown in FIG. 4, the sensor arm 4 is not attached tothe mounting plate 2 of the robot arm 1, but is at a stationary locationand connected to the computer 12. The position of the multi-jointedsensor arm 4 is selected so that both the bone to be sensed and themounting plate of the robot arm 1 moved to its home position are locatedwithin the working space measurable by the sensor arm 4. With the aid ofthe sensor arm 4, at least one reference point on the mounting plate 2can be sensed. By means of the sensor arm 4 both the position and theorientation of the mounting plate 2 and of the sensed reference pointson the patient's bone can be determined in a spatially fixedthree-dimensional coordinate system. The computer 12 transforms thespatial coordinates found into the coordinates of the instrumentcoordinate system. The process can be carried out in such a way that,with the aid of the sensor arm 5, several points on the mounting plate 2are sensed, the positions of which are precisely defined in relation tothe instrument coordinate system. Another procedure consists in movingthe robot arm 1 not to one, but to at least three home positions insequence. In each of these home positions, only one point of preciselyknown and defined position on the mounting plate 2 is sensed with thesensor arm 4. In the spatial coordinate system of the sensorarrangement, this point has different coordinates for each home positionof the robot arm 1. It is also possible to derive from these coordinatesa mathematical rule to define the desired coordinate transformation. Thesensing of the reference points on the bone is only done after thismathematical rule has been determined.

The configuration of the device according to the invention shown in FIG.5 has a manually movable sensor arrangement for three-dimensional objectmeasurement in the instrument coordinate system of the robot arm,consisting of a measuring arrangement 4′ with remote data transfer. Itcomprises a stationary receiver 7, a sensing probe 8 with a firsttransmitter 9 and a second transmitter 10 arranged on the mounting plate2. The transmitters 9, 10 have several signal generators 11 in a rigidlydefined spatial arrangement, which emit positioning signals that arereceived by the receiver 7. From the positioning signals, the positionand orientation of the sensing probe 8 and of the mounting plate 2 isdetermined in a spatially fixed three-dimensional coordinate system. Thespatial coordinates of the sensing probe 8 and of the mounting plate 2thus found can be passed to the computer 12, which transforms thespatial coordinates of the sensing probe into the coordinates of aninstrument coordinate system upon which the program control system isbased.

Locating systems having a measuring arrangement with remote datatransfer are known in principle and can be based on optical, inductiveor ultrasonic processes. The sensing probe has, for instance, a smallplate with four or six infrared light-emitting diodes 11 as signalgenerators arranged at its corners. The light impulses transmitted fromthese are received by the receiver 7 situated stationary in the room,which has three separate receiving elements 13, consisting of optics andlight-sensitive sensors. Making use of the precisely known geometricalarrangement of the transmitter and receiver elements 11, 13, bymathematical evaluation of all the received signals, the position andorientation of the sensing probe 8 can be calculated in the spatiallyfixed coordinate system. According to the invention, a suitable smallplate 10 with transmitter elements 11 is also affixed to the mountingplate 2 of the robot arm 1. In this way, the positions of both thesensing probe 8 and the mounting plate 2 are found, so that the spatialcoordinates of the reference points on the bone sensed with the sensingprobe can be transformed through mathematical transformations into theinstrument coordinate system of the industrial robot upon which theprogram control system is based.

What is claimed is:
 1. A device for positioning and guidance of asurgical instrument during an orthopaedic operation, said devicecomprising: an industrial robot having a program-controlled,multi-jointed robot arm with a mounting plate at an end of the robotarm; an instrument for the orthopaedic operation arm on the mountingplate; a program control system with computer connected to said robot; asensor arrangement for the sensing of reference points on the bones ofthe patient; and sensors in the joints of the robot arm for determiningjoint positions of the robot arm in an instrument coordinate systemdefined in the program control system and such that the robot arm can bemoved by means of the program control system into a working position forthe orthopaedic operation; said sensor arrangement comprising amulti-jointed sensor arm affixed to the mounting plate and forming apassive manually guided measuring instrument, said sensor arm havingsensors for detecting joint positions of said sensor arm, saidinstrument being available to the surgeon during the orthopaedicprocedure such that movement of the sensor arm at a previously-assumedposition of the robot arm defined by the program control system,reference points on a patient's bone can be sensed and the computerdetermines the working position of the robot arm for the orthopaedicoperator from the positional details supplied by the sensors of thesensor arm and the positional details of the robot arm sensors measuredin the instrument coordinate system.
 2. The device according to claim 1,further comprising an additional monitoring arrangement to detect aspatial position of the patient during the operation with a cameradetecting positions of marking pegs inserted in the bone before theoperation, the coordinates of said pegs being sensed with aid of thesensor arm on setting-up of a working position of the robot arm, suchthat positional changes in the marking pegs detected by the camera areprocessed in the computer and a correction is made to the workingposition of the robot arm by means of the program control system.
 3. Thedevice according to claim 1 wherein the instrument is guided on acarriage affixed to the mounting plate so that it is moveable axially.4. The device according to claim 1 wherein the carriage is arranged at afixed angle to the mounting plate.
 5. The device according to claim 1wherein the carriage is movable orthogonally to the mounting plate. 6.Device for positioning and guidance of a surgical instrument duringorthopaedic operations with an industrial robot, having aprogram-controlled, multi-jointed robot arm with a mounting plate at itsend, an instrument for the surgical procedure held on the mountingplate, a program control system with computer, a sensor arrangement forthe sensing of reference points on the bones of the patient, such thatsensors are arranged in the joints of the robot arm for determining thejoint positions in an instrument coordinate system defined in theprogram control system and such that the robot arm can be moved by meansof the program control system into a working position for the surgicalprocedure, said sensor arrangement comprising a multi-jointed sensor armconnected to the computer and in a form of a manually-guided measuringinstrument with sensors for detecting joint positions of said sensor armand so positioned at a fixed location that both a patient's bone to besensed and the mounting plate positioned in a home position lie within arange of the sensor arm, so that, with the aid of the sensor armreference points on the patient's bone and at least one reference pointon the mounting plate can be sensed and the computer transforms thecoordinates of the reference points determined with the sensor arm in aspatially fixed three-dimensional coordinate system into coordinates ofthe instrument coordinate system.
 7. The device according to claim 6,further comprising an additional monitoring arrangement to detect aspatial position of the patient during the operation with a cameradetecting positions of marking pegs inserted in the bone before theoperation, the coordinates of said pegs being sensed with aid of thesensor arm on setting-up of a working position of the robot arm, suchthat positional changes in the marking pegs detected by the camera areprocessed in the computer and a correction is made to the workingposition of the robot arm by means of the program control system.
 8. Adevice for positioning and guidance of a surgical instrument duringorthopaedic operations with an industrial robot, having aprogram-controlled, multi-jointed robot arm with a mounting plate at itsend, an instrument for the surgical procedure held on the mountingplate, a program control system with computer, a sensor arrangement forthe sensing of reference points on the bones of the patient, such thatsensors are arranged in the joints of the robot arm for determining thejoint positions in an instrument coordinate system defined in theprogram control system and such that the robot arm can be moved by meansof the program control system into a working position for the surgicalprocedure, characterized in that the sensor arrangement comprising ameasuring arrangement with remote data transfer, having a stationaryreceiver, a sensing probe with a first transmitter and a secondtransmitter arranged on the mounting plate, the transmitters havingmultiple signal generators in a rigidly defined spatial arrangement thatemit positioning signals received by the receiver, the computertransforming spatial coordinates of the sensing probe determined fromthe positioning signals with spatial coordinates of the mounting platealso determined from the positioning signals into the coordinates of theinstrument coordinate system.
 9. The device according to claim 8,further comprising an additional monitoring arrangement to detect thespatial position of the patient during the operation with at least onereference peg, which can be affixed to the patient's relevant bonebefore the surgical procedure and equipped with a third transmitter,such that the transmitter of the reference peg which is also equippedwith multiple signal generators, emits positioning signals that arereceived by the receiver and processed by the computer for generating acorrection of the working position of the robot arm on transfer to therobot control system to track the robot to the patient.
 10. A device forpositioning and guidance of a surgical instrument during orthopaedicoperations with an industrial robot, having a program-controlled,multi-jointed robot arm with a mounting plate at its end, an instrumentfor the surgical procedure held on the mounting plate, a program controlsystem with computer, a sensor arrangement for the sensing of referencepoints on the bones of the patient, such that sensors are arranged inthe joints of the robot arm for determining the joint positions in aninstrument coordinate system defined in the program control system andsuch that the robot arm can be moved by means of the program controlsystem into a working position for the surgical procedure, characterizedin that the sensor arrangement comprising a measuring arrangement withremote data transfer, having a stationary receiver, a sensing probe witha transmitter, such that the transmitter has multiple signal generatorsin a rigidly defined spatial arrangement, that emit positioning signalsreceived by the receiver, such that, with the aid of the sensing probe,reference points on the patient's bone and at least one reference pointon the mounting plate can be sensed and the computer transforms spatialcoordinates of the sensing probe determined from the positioning signalswith spatial coordinates of the mounting plate, also determined from thepositioning signals into the coordinates of the instrument coordinatesystem.
 11. The device according to claim 10, further comprising anadditional monitoring arrangement to detect the spatial position of thepatient during the operation with at least one reference peg, which canbe affixed to the patients relevant bone before the surgical procedureand equipped with a third transmitter, such that the transmitter of thereference peg which is also equipped with multiple signal generators,emits positioning signals that are received by the receiver andprocessed by the computer for generating a correction of the workingposition of the robot arm on transfer to the robot control system totrack the robot to the patient.